Understanding the effect of a static driving shear stress on the liquefaction resistance of medium dense granular soils

The influence of a driving static shear stress on the liquefaction resistan ce of medium dense granular soils is investigated. A laboratory study of th e behavior of five sands (percentage of silt varying between 2 and 42%, and D-50 varying between 0.55 and 0.09 mm) was undertaken. These five sands we re sampled from the foundations of two dams in Quebec (Canada). Sixty cycli c direct simple shear (DSS) tests were performed with and without a driving static shear stress. Relative densities D-r varied between 60 and 70%, and static shear stress ratios alpha = tau (st)/sigma (vc)' varied between 0.2 and 0.6. The presence of static shear stress increased the cyclic strength of these soils. A relation between alpha and K(alpha) factor giving the ef fect of preshearing on cyclic shear resistance is obtained, The mechanical competence is examined as a function of D-50 and percentage of fines. The o bserved dilatancy yielded rather cyclic mobility than liquefaction. (C) 200 1 Elsevier Science Ltd. All rights reserved.